New world Primates are represented by the suborder Platyrrhini. This includes the families Callitrichidae (marmosets and tamarins), Callimiconidae (Goeldi's monkey) and Cebidae (cebids) with a total of 55 species according to Honacki et al. (285) and Hershkovitz (277). Some authors (69, 393) recognize a larger number of callitrichids. The primates are the best studied and best known group of neotropical mammals, which is why an exhaustive review of the relevant literature would exceed the purpose of this book.

A number of primates are used for food or captured alive or bred for commercial purposes, but there is no outstanding key species in this respect. They will therefore be presented summarily as a group.

Geographical distribution: The Cebidae family ranges from southern Mexico to northern Peru, along the Pacific slope and as far southeast as northern Argentina. The more restricted tropical distribution of the Callitrichidae and Callimiconidae families runs from Costa Rica in the north to southern Brazil (91, 124, 255, 393). Callitrichids achieve their greatest diversity in Amazonian Brazil, Peru and Colombia (Table 24).

Elevational range: Primates are mainly lowland animals but some species of cebids can be found in montane forests up to 3 000 m. The more restricted range of the callitrichids keeps them in tropical forest habitat, rarely above 1 000 m (124, 245, 382).

Size and weight: Adult neotropical monkeys vary in size from 28-35 cm total length, and 120-145 g total weight (Cebuella pygmea) to a top length of 130 cm and a top weight of more than 13 kg for male Brachyteles arachnoides. The callitrichids are small, weighing up to 750 g, while the cebids, excepting the genera Saimiri and Aotus, are generally over 1 kg in weight. The adult males of various cebid species are more corpulent than the females (122, 500, 612).

Habitat: These strictly arboreal animals require wooded habitats. The greatest species diversity is achieved in the moist tropical forests, though some species prefer montane forests or deciduous, secondary or gallery forests with mosaics of open areas (124, 134, 175, 244, 551, 553). Robinson and Ramirez (500) postulate that bigger monkeys generally prefer large primary forest whereas the smaller species are more apt to frequent habitat subject to seasonal or successional change.

Abundance: Ecological research on neotropical primates has received a great deal of attention recently and population estimates for numerous species and sites are therefore available (124, 174, 180, 233, 266, 304, 307, 500, 551, 573). The figures obtained using transect methods or the location and counting of troops of monkeys in specific experimental areas vary widely with species, habitat and the method of reckoning, from 1 to more than 1 000 monkeys per km2. Most estimators give figures of 1-30/km2 but population levels as great as 1 000/km2 are frequent, a demonstration that primates can be quite numerous in more than one neotropical ecosystem. The most abundant genera are Saimiri, Cebuella, Callithrix, Cebus and Alouatta. Density estimates can vary by as much as two orders of magnitude, however, for the same species in different habitats under different hunting pressure (123, 266, 307, 500, 573).

Behaviour: As a group monkeys are tree-dwelling, diurnal (except for Aotus), lively, sedentary and social in habit. They exhibit a great variety of gait, vocalization, habitat utilization and social interaction. Some species are noisy and easy to detect, whereas others tend to flee or are mostly silent.

The callitrichids, Callimico and other cebids such as Aotus. Callicebus and Pithecia live in small family groups made up of a permanent pair and its offspring of various ages. Other cebids customarily live in bigger groups ranging from 5 to 20 or 30 individuals, a more complicated social structure, and are (usually) territorial in habit. Saimiri and Cacajao tend to form even bigger troops of up to 100 monkeys (124, 266, 304, 307, 500, 551).

Feeding habits: Fruits, insects and leaves are the basic items in the neotropical primate diet. Every species apparently consumes at least two of these items (307).

Callitrichids feed on small fruits, insects and the sap of certain trees. Many cebids, e.g. Aotus, Saimiri and Cebus, are omnivores. They are great fruit eaters but also invest long hours looking for food of animal origin, including insects, molluscs, small vertebrates, bird eggs and chicks, etc. The genera Callicebus. Pithecia and Ateles are primarily thought of as frugivores, whereas Lagothrix, Chiripotes and Cacajao are considered to be both leaf-eaters and frugivores. Howling monkeys of the genus Alouatta basically eat foliage but do round out their diet with fruit, buds and flowers (124, 174, 307, 500, 553).

Reproduction: The fairly low reproductive capacity of monkeys is inversely proportionate to their bodily size (500). Callitrichids reach sexual maturity in the second year of life but do not breed so long as they remain in the maternal group. The bigger cebids take 4-8 years to reach sexual maturity. The gestation period ranges from 128-145 days for callitrichids and 157-225 days for cebids. Callitrichids almost always give birth to two young and Callimico and the cebids just one. The interval between successive births may be less than one year for callitrichids, whereas it is one year for the smaller cebids (Saimiri, Aotus. Callicebus) and from one-and-a-half to three years for the big cebids (Alouatta, Ateles, Cebus,Lagothrix), due to their longer suckling regime and period of parental care (93, 122, 124, 265, 382, 500).

Most of the data on primate reproduction comes from animals in captivity. The record of reproductive efficiency and periodicity in the wild is incomplete. Many species apparently breed year-round, but with some degree of seasonality. The smaller insectivore-frugivore species such as the callitrichids Callimico, Aotus, Saimiri and Callicebus are more apt to give birth in the early part of the rainy season (124, 553).

Hunting: Monkeys are hunted for food with guns, bow and blowpipe. Often several monkeys in the same troop are killed but they may not all be recovered because some wounded or dying monkeys cling fast to the branches and remain lodged in the tree (32, 43, 549).

The simplest way to catch a monkey alive is to hunt the female and capture her young. A monkey up a small tree can sometimes be caught by shaking the tree, or, once a troop has been treed, the surrounding trees can be cut down and the monkeys caught as they try to flee along the ground (244, 549). Professional monkey hunters in the Peruvian Amazon use wooden traps baited with fruit, or big vertical nets stretched along a path in a strategic spot. The hunters harry the animals into the net and catch them when they become entangled (549). The captured animals are kept and transported in wooden cages or jute sacks.

Products: Even where monkeys are not officially listed as game animals, their meat is prominent in the diet of indigenous groups and some campesino communities (Tables 5 and 9). Ateles, Lagothrix. Chiropotes and Callicebus are preferred for the quality of their meat but Alouatta, Cebus and Cacajao are very often hunted and eaten too (32, 130, 245, 289, 382, 500, 551). In any case, primate meat is often thought of as an emergency food. Ayres and Ayres (32) mention that monkey hunting is much more frequent on the return journey from an otherwise unsuccessful hunting trip.

Monkeys have traditionally been valued as pets as well as for food. A booming trade began in the year 1950 in answer to the demand for neotropical primates in the industrialized countries for use as pets and for biomedical experimentation (244, 357, 549). The trade peaked in the 1960s (Table 19), when it offered income and employment to traders and campesinos in forest areas in Peru and Colombia, numerically the main export countries. The species most exported were Saimiri sciureus, Aotu trivirgatus. Cebus albifrons, Saguinus oedipus. Lagrothrix lagothrica and Saguinus nigrocollis.

The preferred neotropical primates for biomedical experimentation and their main research uses are (357):

As a precautionary measure to avoid population decline, most countries in the area have stopped exporting primates in recent years. The demand does exist, however, and primate populations do represent a potentially valuable resource.

Management: The three main factors to contend with in primate conservation are: habitat loss and fragmentation through deforestation, hunting for food, and capture for the live animal trade (124, 266, 357, 500, 551).

Though the live animal trade is of little relevance at present, monkeys do continue to be hunted for food. With no effective restrictions the impact may even be greater than that of the massive capture of monkeys for export characteristic of earlier decades (266, 551, 573). It is also and exclusively the larger monkeys that are hunted for their meat, and these are the most vulnerable species: being big, they are easy to detect, and their very low reproductive capacity obviously means a longer recovery. Unrestricted hunting of large monkeys therefore inevitably leads to population depletion, and this is already happening in some regions (17, 307, 551, 573, 608).

Like many other problems of subsistence hunting, this one is social and cultural rather than biological. The most plausible medium-term solution would be to develop and foster the production of domestic monkeys to reduce the need for hunting wild ones. A pilot ecodevelopment plan now ongoing in islands in the vicinity of Iquitos, Peru, combining forest conservation, sustained primate production for live capture and export, environmental management and the extension of technical advice to local people (265), is a relevant example.

As deforestation spreads the situation of arboreal mammals goes critical: deforested areas represent so much lost habitat for monkeys, and the remaining patches of forest become isolated. The survival probabilities of monkeys living there came to depend on the size and diversity of these islands in the forest, and on certain intrinsic characteristics of the primate species. Small unspecialized feeders have a better chance to survive than the big specialized frugivores like Ateles and Lagothrix (307, 500). The IUCN (576) lists 27 neotropical primate taxa as seriously endangered, mostly because their habitats have been irreversibly destroyed.

Captive breeding: Neotropical primates are exhibited in many zoos. Some groups like Cebus. Ateles and various callitrichids can survive and breed successfully in captivity but others, such as Alouatta and Cacajao, present major problems (138, 432, 612). In addition to zoos in Latin America, a number of centres specialize in primate propagation and research (125, 357). The breeding component of the Iquitos primate project in Peru concentrates on producing those species in greatest demand for biomedical experimentation: Saimiri, Aotus and Saguinus (J. Moro, C. Malaga, pers. com.). The Río de Janeiro Primatology Centre focuses on the preservation and propagation of various species and subspecies that are highly endangered in the wild in their southeastern Brazilian habitat (125), whereas research is the top priority of the Argentinian Primate Centre (O.J. Colillas, in litt.).